1. Field
This disclosure relates to the field of communications technologies, and in particular to an estimation apparatus for IQ imbalance of an optical transmitter, a compensation apparatus for IQ imbalance of an optical transmitter and electronic equipment.
2. Description of the Related Art
Coherent optical communications systems have developed rapidly in recent years due to their excellent anti-dispersion performance, the use of dispersion-free compensation optical fibers, and relatively high sensitivity of a receiver. In a high-speed optical communications system, it is generally required to provide a modulator in an optical transmitter to modulate a transmitted signal where in-phase and quadrature (IQ) modulators are widely used in optical communications systems to generate transmitted signals of high spectral efficiency.
FIG. 1 is a schematic diagram of a modulator of an optical transmitter in the related art. As shown by a dotted box in FIG. 1, a modulator 101 of the optical transmitter has two Mach-Zehnder modulators (MZMs), respectively referred to as a first Mach-Zehnder modulator 102 and a second Mach-Zehnder modulator 103, and a phase modulator (PM) 104, the first Mach-Zehnder modulator 102 and the second Mach-Zehnder modulator 103 being respectively used for modulating driving signals vrf,I and vrf,Q of an I path and a Q path, and the phase modulator 104 introducing a phase difference of 90° between the I path and the Q path. Due to changes of ambient temperatures, and device aging, etc., drifts may possibly occur in three bias points (denoted by bias I, bias Q and bias P) of the modulator, which may make them deviated from an optimal working points. In order to ensure a modulation performance of the modulator, bias voltages VI, VQ and VP on the three bias points, bias I, bias Q and bias P, are controlled according to a result of detection of an output optical field of the modulator 101. And furthermore, as the signals of the I path and the Q path experience different paths, magnitudes of their relative power usually change at an output end of the modulator 101, and such a change is referred to as IQ amplitude imbalance of the optical transmitter.
Generally, a phase offset drift and an amplitude imbalance of the optical transmitter end are collectively referred to as optical transmitter IQ imbalance; wherein, both the phase offset drift and the IQ amplitude imbalance have effects on a shape of a constellation diagram of the received signals and increase bit error rates. FIG. 2 is a schematic diagram of the effect of the optical transmitter IQ imbalance on the constellation diagram of the received signals. As shown in FIG. 2, the constellation diagram on the left side denotes the transmitted signals, and the constellation diagram on the right side denotes the received signals. And due to the effect of the optical transmitter IQ imbalance, the constellation diagram of the received signals at the receiver end becomes a distorted parallelogram.
In an existing method, estimation and compensation of the IQ imbalance are generally performed based on Gram-Schmidt orthogonalization (GSOP), in which received signals of the I path or the Q path are taken as reference signals.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.